Pressure measuring instrument



July 27, 19 3' A. F. ALLWEIN ETAL PRESSURE MEASURING INSTRUMENT File d Oct. 17, 1941 FIG. I.

INV

' ENTOR. ALOYSIUS .ALLW IN F. E v gm ments' Patented July 27, 1943 T'V'OFFICE i PRESSURE MEASURING INSTlbUMENT Aloysius F. Allwein and Edwin C. Burdick, Philaq delphia, Pa., i'nen't Company, tion 01' Pennsylv assignors to The.Brown Instru- Philadelphia, Pa., a corpora- Application ottom- 17, 1941, Serlal No. 415,372 8 Claims. (01. 13-110) The present invention relates to pressure gauges and more particularly to that type of pressure gauge which is used to measure pressures that are below or slightly above atmospheric pressure and are commonly known as absolute pressure gauges. V

In thepast a great deal of difllculty has been experienced in obtaining a pressure responsive element that was sensitive enough to record minute variations in pressure and at the same time be strong and rigid enough to withstand the forces produced by an absolute vacuum. It has also been a problem to accurately calibrate van instrument of this type and to transfer the moveof the pressure responsive element to a recording element whereby a very small 'movement of the former can move the latter through a comparatively large distance. r

It is accordingly an object of the present invention to provide an absolute pressure gauge that is rugged and accurate and one which may easily be calibrated.

It is a further object of the invention to pro vide in a measuring instrument a linkage be- ,tween the pressure responsive. element and an indicating element which is easily adjustable to properly calibrate the instrument and which may connected to the interior of the.

be adjusted to compensate fol-individual differences between various pressureresponsive elements. It is a further object oi the invention to devise a connecting link to be used in a measurins instrument that in a small space.

is compact and may be used 1...

A further object of the invention is to pro-'- vide a n l Way to join two expansible chembers together. V

The various features of novelty which characterize this invention are pointed out with particularity in the claims annexedto and forming a part of this speciflcatio For a better understanding of theinvention. however. its advantages and specific obiects obtained with its use.

to the accompanying 1 reference should be had drawing and descriptive matter in which is il1ustrat'ed and described a preferred embodiment of the invention.

0! the drawing:

Fig. l is a front view. partiyin section, oi ai embodying my invention..

measuring instrument and Fig. 2 15a top view oi the pressure responsive element and connecting linkage.

Referring to the drawing, there is shown in Fig. l a casing i having a pressure'respoifizg f unit I supported against itsback wall,

- The pressure responsive unit pressures to be measured, .is formed "ment together. It will the lower Chamber, ,l'iowever, theconnection the pressuresinoe the tube unit is used to adjust an exhibiting element 8 through a suitable connecting linkage. This exhibi ing element is attached to a shaft 4 which is mounted in bearings in the instrument'casin'g consists .ojfj 1 I evacuated chamber A which isformed by a rigid support 5 that is fastened to the casing rear wall. This support has a projection Sexten'ding down: wardly therefrom and is provided with a spring; seat formed by the corner between the support I 5 and the beginning of the j projection. The chamber is completed y means of a bellows i, whose open end is placed in a groove formed in the support 5 and'which is soldered thereto. Be-

fore the bellows is soldered to the support, a ree inforcing member 8, also having a spring seat formed on it, is soldered or otherwise suitably.

bellows at the this assembly is I center of its end wall. When made the bellows is evacuated through atube-Q to as near a complete vacuum as possible and then sealed oil by means of a drop of solder ii); A second chamber B, which is subjected to the by stationary support ii that has an opening il in it, which opening is connected with the pressure source by means of a tube i3. Fastened. to this support ii is a second bellows i4 whose open end is placed in a'sroove in the support ii and soldered in position. Before the bellows is solderedto the support, however, a cylindrical reinforcing membar I! is attached to its end wall in a manner similar to t in which the member 8 is ias f tened to'tliebellows ll. v --A plate I 'iaplaced between the two bellows end wall and is interred in position by means of a screw I! which is insertedthrough the opening- I! and the reinforcing member ii and then threaded 'into the reinforcing member: 8. When this screw is tightened it wiil connectjthe two bellows end walls and the plate It ior'movebe noted that the rein-" 1 forcing member 8 does not have an opening com-V h pletely throughit. This is for the reason that inorder to obtain and' keep a complete'vacuum in the upper chamber no more openin'gs absolutely necessary should bemade therein.. In

formed by-the screw II is suillcient to maintain ms continuailyco nectet-lv to the pressure source. "The screw, no ever. is formed withan inclined surface 18 sure leakage in the lower chamber. A drain tube 20 is inserted through the supporting member II at the lowest point of the chamber B so that any condensate which might form in the chamber can be drained therefrom in order to keep the chamber its original size. The tube 20 can be provided with a suitable valve that may be opened when the draining is to take place or may be connected to the pressure source. In order to make the pressure responsive unit more rigid and to prevent any possible movement of the supporting members and II toward each other four reinforcing rods 2I are used. One of these rods is in each corner of the supporting members 5 and II as is best shown in Figure 2. In view of the fact that the upper chamber A is evacuated while the lower chamber B is subjected to ,the

pressure to be measured, any change in pressure I in the lower chamber will cause a movement of the plate I6.

Movement of the plate I6 is proportional to the pressure being measured and is transferred to the exhibiting element 3 by means of a linkage comprising wires 22 that are fastened to the plate I2. These wires are fairly stiff and are connected at their upper ends by means of a cross-member 22-whose ends are bent over as shown at 24 in Fig. 2. Screws 2! are then threaded into the cross-member and the heads of these screws cooperating with the bent over ends 24, grasp the wires 22 and hold them rigidly in place. After the wires have been adjusted to their proper length a drop of solder may be placed thereon to prevent any movement thereof.

A lever member 26 that is pivoted to -a shaft 21 has its left end pivotally attached to the center portion of the cross member 23 so that as 22 moves up and down the lever will be moved around its pivot. The pivot for the lever is formed by means of a shaft 21 that is iournalled in bearings 28 and-29 which form a part of the upper supporting member I. The bearing 22 is provided with a screw member 22 that has a socket to receive the front end of the shaft 21 and which can be adjusted to vary the end play moves. It is noted that as the lever. 26 turns around its shaft the wires 22 will bend slightly by a sleeve is a lever II which has a bent over end 22 that is held in engagement with the upper surface of the right end of lever 2' by means of a spring 22. This'causes the arm II .and shaft 21 to follow movements of the plate I4 andalsoserves to keep the wires 22 under tension so that therewillbenoplayintheleversystem. Alsoattached to the shaft 21 is an angularly shaped lever 24 whose left end has a turned over portion 24. An adjusting screw 28 is threaded through this end portion and abuts against a stop 21 formed on the support 4. By adjusting the screw 24 the movement of the lever 24 in acounter clockwise direction can be, limited. This position will be determined by the minimum pressure to which the bellows I4 is to be subjected.

An arm 32 is pivoted at 22 to the downwardly extending portion ofthe lever 34 and acts as an extension of that lever. This arm can be adwith respecttoleverllbymeansofa screw 40 that passes through a turned-up edge 2,325,091 r ei nforcing member so that there will be no preson the arm and is threaded into a turned-up edge 42 on the lever 34. By rotating the screw 40 the angular position of arm 38 can be adjusted with respect to the arm 34. A spring 43 is placed around the screw 40 in order to hold that screw in its adjusted position and in order to maintain the parts H and 42 in their proper relatiocn, depending upon the adjustment of the screw. A yoke member- 44 is fastened to the lower end of the arm 38 and has journalled in its up-standing ends a screw 45. This screw serves to position a slider 46, that is also U- shaped in form, and which bears against the yoke with its legs in engagement with the threads of the screw, so that this slider can be moved various distances from the shaft 21 as the screw 45 is rotated. Movement of the lever 34 and arm 28 around the pivot 21 acts to adjust the exhibiting element 3 by means of a connecting link 41 and an arm 48 which is attachedto the shaft 4. The arm 48 is-provided with a plurality ofholes through any one of which the connecting link 41 may extend.

An absolute pressure gauge isv used to measure absolute pressure rather than gauge pressure, as is usually the case. Therefore, some means is provided to compensate for the atmosphere. It is for this reason that the two opposed chambers A and B are used. Since the atmosphere is of this shaft and the freedom with which it acting on the outside of each of the bellows which form the chambers and which are as near identical as possible, its effect will be cancelled out, and the differential pressure within the chambers will produce movement of the plate I8.

In calibrating an instrument various things have to be taken into account such as total movement of the exhibiting element, the bellows characteristics, their area and the range of the instrument. When the bellows 1 is evacuated it will collapse until the'projection G and member 8 engage to limit its minimum length. If a vacuum is also applied to the bellows I4 the plate It will be moved downwardly to some definite position since, disregarding the difference in the bellows characteristics, one vacuum will balance the other, and the exhibiting element, will indicate zero pressure. Since it is ordinarily desirable, however, to have the mid-position ofthe bellows and plate I6 represent the mid-point on the instrument scale instead of its end some means must be provided to elongate the bellows 1 relative to the bellows I4 when the latter has zero pressure in it. To this end a spring 48 is placed 'in the bellows 1 with its ends on the spring seats formed on parts 6 and 8. By making the spring of different lengths the zero point of the exhibiting element can be changed.

A second and more important function of the spring 49 is to determine the range of the instrument. Suppose both bellows are evacuated and a small amount of air is allowed to enter bellows I4, the bellows 1- would then be compressed a certain amount. If the force of spring 49 isadded tothe natural resiliency of the bellows the same amount of air in bellows I4 will produce a smaller compression of bellows 1 and movement of the plate I0.- Therefore the strength of spring 49 will determine the amount of travel in plate It for a given pressurechange in bellows I4. The stiffer the spring, the larger the range of the instrument since a larger pressure change will be required to move plate It a given amount. 7

It is practically impossible to get bellows that have the same area and also the same pressurepressure-length curve full range movement of plate leigth curves. That is each bellows will compress different amounts with the same force applied to it. In most cases, however, the shape of the is similar for different bellows. For this reason the nuts on the upper ends of supporting rods 2| are adjusted until the bellows l and I4 have been compressed to a point that they will be operated through a desirable portion of their curves. The support II is so mounted on the casing i that it may be adjusted enough to take care of the necessary compression 'of the bellows.

After. the pressure responsive unit has been i to the free ends of assembled it is placed in the casing along with the linkage between the unit and the exhibiting element. It is then necessary to calibrat the instrument. First, the right end of link 41 is placed in one of the openings of the arm 48 to obtain the correct angle between these two parts for the range of the instrument and the portion of the bellows pressure-length curve that is to be used.

No matter whether the instrument is an indicator or a recorder the exhibiting element has to have some given zero point and move through a given distance. After the parts 41 and 48 have been connected the screws are loosened and the cross-member 23 is shifted up and down on wires 22. cross-member is moved until the element 3 is approximately at its zero scale position, which, in this case, will be as shown with the element 3 at the right end of its travel. The screws 25 are then tightened and a drop of solder placed over each connection to prevent relative movement of the parts. A final zero adjustment is obtained by rotating screw to vary the angular relation 'of lever 3 and arm 38.

Due to the different characteristics of different bellows some provision must be made to vary the angular movement of the element 3 for a given l5. This is obtained by rotating screw to move slider 46 in yoke M. This adjustment varies the effective length of arm 38 and therefore the movement of element 3 for a given displacement of the plate It.

For the sake of appearance of the completed instrument it is often desirable to place a cover over the front of the measuring unit. To this end a shield 50, shown only in Figure 2, may be fastened to the supports 5 and Ii extend around the two sides and front of the bellows.

While in accordance with the provisions of the statutes, we have illustrated and described the best form of this invention now known to us, it would be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of this invention as set forth in the appended claims, and that in some cases certain features of this invention may sometimes be used to advantage without a corresponding use of other features.

Having now described our invention, what we claim as new and desire to secure by Letters Patent is:

1. In a measuring instrument, the combination of a pair of expansible chambers mounted with one end of each chamber in a fixed position and the opposite end of each chamber in abutting relation and free to move, a member interposed between said abutting ends andmovable therewith, means to rigidly fasten said ends and member together, a pair of stifi, flexible links fastened to spaced points on said member and extending in the same direction beyond the fixed end of With zero pressures in chamber B the a cross-member attached said links, to move theremoves, a pivoted lever atthe center of said crossone of said chambers,

with as said member tached at one end to member, the arrangement being such that as the lever moves around its pivot the links will flex, 1

an arm biased into engagement with said lever to follow the movements thereof, and an exhibiting element operated by said arm.

2. In a measuring instrument the combination of a pair of expansible chambers mounted end to end with the outer fixed against movement, a between the adjacent ends plate member inserted of said chambers and r movable therewith as'the pressure in said chambers changes to change the size of said chambers, an exhibiting element, means to move said exhibiting element in response to movement of said plate including a pair of flexible members each attached at one end to spaced points on said plate and extending beyond the fixed 'end of one of said chambers, a' cross-member attached to the other end of said flexible members, and connections between said cross-member and said exhibiting element.

3. In a measuring instrument, a pair of expansible chambers, each of said chambers comprising a bellows having a closed end wall, means to fasten said end walls together comprisinga first reinforcing member attached to the inner end wall of one of said bellows, said end wall and member having an opening formed therein, a second reinforcing member fastened to the inside 'wall of said second bellows, the second reinforcing member and bellows end wall having an opening extending therethrough with a sharp edge formed inside the opening of said second reinforcing member, a fastening member extending through the opening in the second reinforcing member and into the opening in the first reinforcing member, said fastening member being formed with an inclined face that abuts against said sharp edge in the second reinforcing member to form between.

4. In a measuring instrument comprising a pair of expansible chambers each formed of a bellows having an end wall, means to fasten the end walls together comprising reinforcing members fastened to the inside of ing member extending from the inside of one bellows through its reinforcing member and end wall, through the end wall of the second bellows and into said second reinforcing member, whereby said bellows end walls will move together.

5. An absolute pressure gauge comprising a first evacuated bellows mounted with one end free and one an fixed, a second bellows subjectecl to a pressure to be measured also having one end free, the bellows being so arranged that their free ends abut each other,

an opening in the bellows wall, a second reinforcing member attached to the inside of the second bellows, said second reinforcing member being threaded into the opening in said first reinforcing member, said fastening member and second reinforcing member being so relatively shaped that there is a pressure tight connection between them.

ends of each chamber a pressure tight connection thereeach end wall and a fasten- 6. In a measuring instrument, the combination of a member movable in response to variations in the value of ajcondition, an exhibiting element, means to move said element by said member comprising a pair of flexible links attached to said member, a cross-piece adjustably attached to the links, a lever mounted for movement around a pivot, means to move said lever by said cross-piece, an arm pivoted to said lever, means to adjust said arm angularly with respect to said lever, a slidable connection on'said arm, a link attached to said connection and operable to move said element.

7. In a measuring instrument, a member movable in response to variations in a condition, an exhibiting element, means to move said element by said member including a pair of flexible links connected atone end to spaced points on said member, a cross-member connected to the other ends of said links to form a parallelogram, a pivoted lever attached at one end to said crosssaid element.

member, means to bias said lever in a direction to keep said links under tension, and connecting means between said lever and element.

8. In a measuring instrument, a member movable in response to variations in a condition, an exhibiting element and means to connect said element for movement by said member comprising a pair of stiff wire links connected at one end to spaced points on said member, a crossmember adapted to be fastened selectively to one of diflerentrpoints along the length of each of said links to form with the links and member a parallelogram, a pivoted lever connected at one end to the mid-point of said cross-member, an arm acting on the other end of said lever in a direction to maintain said links under tension, and adjustable means to connect said arm to ALOYSI-US F. ALLW-EIN. EDWIN c. BURDICK. 

